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| author | Ian Lynagh <igloo@earth.li> | 2012-02-26 01:46:06 +0000 |
|---|---|---|
| committer | Ian Lynagh <igloo@earth.li> | 2012-02-26 13:04:44 +0000 |
| commit | ae04bd43a2640e17a9035f170d76dae356082f88 (patch) | |
| tree | f17b95d0840f4ee66ee622c03da1a96058ade347 /docs | |
| parent | 9065bdbf5299097263c35f6e389b018806f6753e (diff) | |
| download | haskell-ae04bd43a2640e17a9035f170d76dae356082f88.tar.gz | |
Implement "value" imports with the CAPI
This allows us to import values (i.e. non-functions) with the CAPI.
This means we can access values even if (on some or all platforms)
they are simple #defines.
Diffstat (limited to 'docs')
| -rw-r--r-- | docs/users_guide/ffi-chap.xml | 22 |
1 files changed, 20 insertions, 2 deletions
diff --git a/docs/users_guide/ffi-chap.xml b/docs/users_guide/ffi-chap.xml index b5ae0e06e4..34c2b35a3a 100644 --- a/docs/users_guide/ffi-chap.xml +++ b/docs/users_guide/ffi-chap.xml @@ -169,8 +169,7 @@ foreign import ccall interruptible declarations, e.g. <programlisting> -foreign import capi - "header.h f" :: CInt -> IO CInt +foreign import capi "header.h f" f :: CInt -> IO CInt </programlisting> Rather than generating code to call <literal>f</literal> @@ -182,6 +181,25 @@ foreign import capi </para> <para> + When using <literal>capi</literal>, it is also possible to + import values, rather than functions. For example, + +<programlisting> +foreign import capi "pi.h pi" c_pi :: CDouble +</programlisting> + + will work regardless of whether <literal>pi</literal> is + defined as +<programlisting> +const double pi = 3.14; +</programlisting> + or with +<programlisting> +#define pi 3.14 +</programlisting> + </para> + + <para> In order to tell GHC the C type that a Haskell type corresponds to when it is used with the CAPI, a <literal>CTYPE</literal> pragma can be used on the type |